polycarbonate

polycarbonate (PC), a tough, transparent synthetic resin employed in safety glass, eyeglass lenses, and compact discs, among other applications. PC is a special type of polyester used as an engineering plastic owing to its exceptional impact resistance, tensile strength, ductility, dimensional stability, and optical clarity. It is marketed under trademarks such as Lexan and Makrolon.

PC was introduced in 1958 by Bayer AG of Germany and in 1960 by the General Electric Company of the United States. As developed by these companies, PC is produced by a polymerization reaction between bisphenol A, a volatile liquid derived from benzene, and phosgene, a highly reactive and toxic gas made by reacting carbon monoxide with chlorine. The resultant polymers (long, multiple-unit molecules) are made up of repeating units containing two aromatic (benzene) rings and connected by ester (CO-O) groups: .

Mainly by virtue of the aromatic rings incorporated into the polymer chain, PC has exceptional stiffness. It is also highly transparent, transmitting approximately 90 percent of visible light. Since the mid-1980s this property, in combination with the excellent flowing properties of the polymer when molten, has found growing application in the injection-molding of compact discs. Because PC has an impact strength considerably higher than most plastics, it is also fabricated into large carboys for water, shatterproof windows, safety shields, and safety helmets.